Radio transmission



May 2, 1939. J. 1.. GETAZ RADIO TRANSMISSION Filed May 2'7, 1956 ATTORNEY Patented May 2, 1939 UNITED STATES ATENT OFFIE 22 Claims.

This invention relates to the electrical transmission of intelligence signals, such as sound signals, particularly to contraction of volume of sound transmitted and expansion of volume 0 sound received.

The purposes of this invention are as follows:

1. To provide automatic means in transmission for contracting the peaks of volume at the transmitter.

2. To provide automatically in transmission a rate of amplification for very weak sounds which is greater than the amplification used for louder sounds.

3. To provide automatic means in transmission for holding the rate of amplification constant for all sounds except those which are louder than a maximum standard and those which are weaker than a minimum standard.

4. To provide means at the receiving set for restoring sounds received to their original relative volume.

In Figure 1 is shown a diagram of control circuits at the transmitter.

In Figure 2 is shown a diagram of circuits in the receiving set for restoring the original relative volume.

In the methods of transmitting now in use it is customary to control manually the amplification, so as to reduce the rate of amplification for those loudest portions of the program being transmitted, and thus eliminate the peaks of amplitude in the transmitting circuits. It is also customary in transmitting to increase the rate of amplification for very weak signals so that they will be greater than noises which may be introduced in the circuits.

Some receiving sets have volume expanders which increase the volume of the louder sounds and reduce the volume of the weaker sounds to compensate for the changes made at the transmitter as mentioned above. These volume expanders control the rate of amplification by the volume of the detected signals. They increase the rate of amplification of the louder signals and reduce the amplification of the weaker signals without any means of comparing these changes in volume with those changes which may have been made at the transmitter.

There are also automatic means for contracting volume at the transmitter, but these automatic means now in use reduce the volume of all loud signals and increase the volume of all weak signals. The automatic contraction of volume at the transmitter as now used gives a distortion throughout the Whole range of volume.

In this invention. automatic means are shown and described for reducing the loudest sounds which are above a certain maximum standard of volume and increasing the weakest sounds, which are below a certain minimum standard 5 without disturbing the relative volume of the wide range of sounds in between these two standards which are set for the loudest and the weakest signals which is desirable to transmit. This will enable those receivers which are not equipped go with volume expanders to receive all out the loudest and weakest sounds in their original relative volume. It will perform. automatically a contraction of volume similar to that now performed manually.

It will also provide means for expanding the volume at the receiver in the same degree at which it was contracted at the transmitter. That is, it will expand those signals which exceed a certain volume as compared with the carrier and contract those signals below a certain volume, and leave the volume of signals between these two extremes at their original relative strength.

The principles of this invention may be applied to any means for the transmission or reproduction of sound in which electrical signals are used to represent the sound waves. These principles may be used for reproducing sound with phonograph records and motion picture films, as well as by radio.

In Figure 1 the transmitter circuit contains the transmitter 1, battery 2, and transformer 3. The secondary of this transformer is connected to the grid and filament of the triode 5 in which H the current is amplified. The plate circuit of the triode 3 contains the battery It and the transformer ii, the leads [8 and ill of the secondary of this transformer are connected to the transmitter modulator. This plate circuit also contains a transformer it: which is connected to the plate and filament of the diode i l. The circuit of this diode contains the resistance i2 which is by-passed by the condenser it. The current of this circuit is an envelope of the current produced by the microphone, its amplitude being proportional to the strength of the sound signals, and also proportional to the drop in voltage across the resistance E2. The battery i i producesaconstant voltage across the resistances 9 and It which are in series. The negative side of resistance H0 is: connected to the filament of diode I and the plate of this diode is connected directly to the filament of triode 5. The negative side of resistance 9 is connected to the plate iii) of diode 8 and the filament of this diode is also connected directly to the filament of triode 5. The negative side of resistance i2 is connected directly to the grid of triode 5. A very high resistance G connects the filament and grid of triode 5. The positive end of resistance It is connected to the positive end of resistance l8. The negative end of I is connected to the positive end of 9. These connections to the grid and filament of triode might be made to similar grids and filaments in several stages of amplification.

The operation of these circuits are as follows. Let at equal the drop in voltage across the resistance l2 when the loudest sound which it is practical to transmit is being transmitted. That is, when the amplitude of the modulating current is equal to half of the amplitude of the carrier. Let y equal this drop in voltage when the weakest signal is being transmitted which. it is practical to transmit. That is, when the amplitude of the modulating current is two percent of the carrier amplitude. The resistances 9 and it are in a circuit of constant voltage and the resistance It is so adjusted that the drop in voltage across this resistance is greater than y say 2 times 1 The resistance 9 is so adjusted that the combined drop in voltage across both 9 and Hi, from the positive end of ID to the negative end of 9, is less than at, say .80 times a. For the ratios of amplification assumed above the ratio of the resistances B to 9 would be 4 to '76.

If the sound being transmitted produces a drop in voltage across l2 greater than .8050, the negative end of M will be more negative than the negative end of 9, and through the connections shown, including diode 8, the grid of triode 5 will be made more negative and the amplification be reduced. When the drop in voltage across I2 falls below .8030 due to decrease in amplitude of the signal, the rate of amplification will be normal and will not be affected by the voltage drop across these resistances as the diode 8 acts as a one way valve.

However if the amplitude of the signal decreases until the drop in voltage across the resistance I2 is less than 23/, the negative end of It is more negative than the negative end of i2 and through the connections shown, including 5 diode I, the filament of triode 5 will be made more negative with respect to the grid and the amplification will be increased. When the drop in voltage across l2 rises above 2y, the rate of amplification will be normal and will not be aifected as the diode T also acts as a one way valve but in the opposite direction from diode 8.

The action of these circuits may be summarized as follows. For values of amplitude of the signal corresponding to voltages across resistance i2 from 2y to .803: the rate of amplification of the triode 5 will be normal and the amplitude of the signals will be transmitted in the same relative amplitude as originally produced without distortion. This would cover a range of amplitude of the modulating current from 4 percent to 80 percent of the amplitude of the carrier current, or such other range as might be tire-determined. For very loud signals which produce voltages across l2 greater than .SOm the amplification will be contracted, the amount of contraction being increased as the loudness of the signals increases. For very weak signals which produce voltages across [2 less than 2y the amplification will be increased inversely with the strength of the signal.

In Figure 2, the receiving set is shown with two stages of radio amplification. The aerial 50 is connected to the first circuit containing transformer 5i, pentode 54, condenser 53 and battery 55. The second circuit contains transformer 56, pentode 59, condenser 58 and battery 60. The detector circuit contains transformer 61, diode 65, condenser 62 and resistance 6 which is bypassed by condenser 63. The first stage of audio amplification contains the triode 83, battery 85, transformers 6B and 84. The second stage of audio amplification contains the triode 61, condenser 68, battery l0 and. transformer 69, the leads 85 and SI connect to the loud speaker. The secondary of the transformer 84 is connected to the plate and filament of diode ii. The circuit of the diode contains the resistance '53, which is by-passed by the condenser 12, and this circuit produces an envelope. The amplitude of this envelope is proportional to the strength of the audio signals received, and is proportional to the drop in voltage across the resistance 13.

Connected also to the ends of resistance 64 is a circuit containing the resistance H and the resistances it and in series which are lay-passed by the condenser 82. The low frequency component of the rectified current passes through the condenser 82 and the drop in voltage across the combined resistances l8 and 15 is proportional to the direct component of this current, and proportional to the amplitude of the carrier frequency. The positive end of resistance 16 is connected to the positive end of resistance 13. These resistances may be adjusted so that the drop in voltage from the positive end of E6 to the negative end of '55 is proportional to the amplitude of the original carrier current and the drop in voltage across 73 is proportional to the amplitude of the original modulating current. The ratio of resistances T6 to 15 is 4 to 76, the same as the ratio of resistances H) to 9 in Fig. l.

The negative end of resistance 16 is connected to the filament of diode 19. This diode operates as a one way valve and its plate is connected to the grid of triode 61. The negative end of resistance 15 is connected to the plate of diode 18. This diode operates as a one way valve and its filament is also connected to the grid of diode 61. The negative end of resistance 13 is connected to the filament of triode 61. The grid and filament of triode 61 are connected by a very high resistance 14.

The expansion of volume in this receiving circuit operates as follows:

If the drop in voltage across 13 is greater than the drop in voltage across 16 and '15, the negative end of 15 is positive with reference to the negative end of 1'3, the grid of triode 67 is made more positive and the rate of amplification is increased. Thus rcstoring the contraction in modulation which had been made at the transmitter. If this drop across 13 is less than the drop across iii and T5, the amplification will not be affected as tube i8 acts as a one way valve.

However if the signal is so weak that the drop across is less than the drop across 16, the negative end of 13 will be more positive than the negative end of 16, the filament of the triode 61 is made more positive with reference to the grid and the amplification is reduced. Thus restoring the weak signal to its relative strength before its amplification was increased in the transmitter.

The volume control circuits in the transmitter and receiver are essentially the same, but the connections to the grid and filaments of the amplifying tube 6'! are reversed from the connections to 5.

, This invention is shown and described as referring to the transmission and reproduction of electrical signals which represent sound signals. It is apparent that it may be applied to electrical signals which represent other forms of intelligence signals besides sound, and it is intended to include the control of electrical signals which are used to transmit intelligence in any form.

I claim:

1. In a system for transmitting signals, a transmitter circuit, a circuit for amplifying said signals coup-led to said transmitter circuit, two sources of constant voltage of different intensity, means for comparing the voltage produced in said amplifying circuit with said constant voltages, means for amplifying said signals at a constant rate of amplification if said voltage produced in said amplifying circuit is between said constant voltages, and automatic means for reducing said rate of amplification if the voltage produced in said amplifying circuit is greater than said constant voltage of greater intensity, and for increasing said rate of amplification if the voltage produced in said amplifying circuit is less than said constant voltage of less intensity.

2. In a system for transmitting signals, a transmitter circuit, a circuit for amplifying said signals coupled to said transmitter circuit, a source of constant voltage, means for comparing the voltage produced in said amplifying circuit with said constant voltage, means for amplifying said signals at a constant rate of amplification if said voltage produced in said amplifying circuit is greater than said constant voltage, and automatic means for progressively increasing said rate of amplification if said voltage produced in said amplifying circuit is less than said constant voltage.

3. In a system for transmitting signals of variable intensity, a means of amplifying said signals, a high standard of intensity and a low standard of intensity for said signals, means for amplifying said signals at a constant rate of amplifica tion if the intensity of said signals is between said standards, automatic means for reducing the rate of amplification when the intensity of said signals is greater than said high standard, and automatic means for increasing the rate of amplification when the intensity of said signals is less than said low standard.

4.. In a system for' transmitting signals of variable intensity, a carrier medium, a means for modulating said carrier medium with said signals, a receiving circuit, means in said receiving circuit for separating said signals from said carrier medium, means for comparing the intensity of said signals with the intensity of said carrier medium, means in said receiving circuit for amplifying said signals at a constant rate of amplification when the intensity of said signals is less than a given proportion of the intensity of said carrier medium and means for increasing said rate of amplification when the intensity of said signals is greater than said proportion of the intensity of said carrier medium.

5. In a system for transmitting signals of variable intensity, a carrier medium, a means for modulating said carrier medium with said signals, a receiving circuit, means in said receiving circuit for separating said signals from said carrier medium, means for comparing the intensity of said signals with the intensity of said carrier medium, means in said receiving circuit for amplifying said signals at a constant rate of amplification when the intensity of said signals is greater than a given proportion of the intensity of said carrier medium, and means for reducing said rate of amplification when the intensity of said signals is less than the said proportion of the intensity of said carrier medium.

6. In a method of transmitting electrical signals of variable intensity which comprise amplifying said signals in a tube having grid and filament connections, obtaining a direct current voltage which is variable in pro-portion to the amplitude of said signals, generating a voltage which is a standard for comparison with said variable voltage, connecting the difierence of said voltages to the grid and filament of said tube through a one way valve thereby changing the potential between the grid and filament of said tube when said variable voltage is less than said standard voltage, and leaving said potential unchanged when said variable voltage is greater than said standard voltage.

7. In a method of transmitting electrical signals of variable intensity, which comprises, generating a high standard of intensity and a low standard of intensity, amplifying said signals at a constant rate of amplification when the intensity of said signals is between said standards, automatically amplifying said signals at a lower rate of amplification when the intensity of said signals is greater-than said high standard, and automatically amplifying said signals at an increased rate of amplification when the intensity of said signals is less than said low standard.

8. In a method of receiving electrical signals of variable intensity, on a modulated carrier wave, which comprises, comparing the intensity of said signals with the intensity of said carrier wave, amplifying said signals at a constant rate of amplification when the intensity of said signals is less than a certain proportion of the intensity of said carrier wave, and amplifying said signals at a greater rate of amplification when the intensity of said signals is greater than said proportion of the intensity of said carrier wave.

9. In a method of receiving electrical signals of variable intensity, on a modulated carrier wave, which comprises, comparing the intensity of said signals with the intensity of said carrier wave, amplifying said signals at a constant rate of amplification when the intensity of said sig nals is greater than a certain proportion of the intensity of said carrier wave, and amplifying said signals at a less rate of amplification when the intensity of said signals is less than said proportion of the intensity of said carrier wave.

10. In a method of receiving electrical signals of variable intensity, which comprises, generating a high standard of intensity and a low stand ard of intensity, amplifying said signals at a constant rate of amplification when the intensity of said signals is between said standards, automatically amplifying said signals at a higher rate of amplification when the intensity of said signals is greater than said high standard, and automatically amplifying said signals at a lower rate of amplification when the intensity of said signals is less than said low standard.

11. In a system for transmitting signals of variable intensity, a transmitting station, a receiving station, standards of intensity in said transmitting station and said receiving station less than the average intensity of said signals, means for amplifying said signals at said transmitting station, means for amplifying said signals at a constant rate of amplification when the intensity of said signals is greater than said standard intensity, means for amplifying said signals at an increased rate of amplification when the intensity of said signals is less than said standard of intensity, means in the receiving station for receiving said signals, and means for amplifying said signals at a constant rate of amplification when the intensity of said signals is greater than said standard of intensity in said receiving station, and means for amplifying said signals at a reduced rate of amplification when the intensity of said signals is less than the intensity of said standard in said receiving station.

12. In a system for transmitting signals of variable intensity, a transmitting station, a receiving station, standards of intensity in said transmitting station and said receiving station greater than the average intensity of said signals, means for amplifying said signals at said transmitting station, means for amplifying said signals at a constant rate of amplification when the intensity of said signals is less than said standard intensity, means for amplifying said signals at a reduced rate of amplification when the intensity of said signals is greater than said standard of intensity, means in the receiving station for receiving said signals and means for amplifying said signals at a constant rate of amplification when the intensity of said signals is less than said standard of intensity in said receiving station, and means for amplifying said signals at an increased rate of amplification when the intensity of said signals is greater than the intensity of said standard in said receiving station.

13. In the transmission of electrical signals of variable intensity, means for amplifying said signals, a source of constant voltage, means for obtaining a voltage which varies with the intensity of said signals, means for obtaining a control voltage by combining said constant voltage and said variable voltage, means for controlling the rate of said amplification by said control voltage when said variable voltage is less than said constant voltage, and means'for discontinuing said control voltage when said variable voltage is greater than said constant voltage.

14. In the transmission of electrical signals of variable intensity, means for amplifying said signals, two sources of constant voltage of different values, means for obtaining a voltage which varies with the intensity of said signals, means for obtaining a control voltage by combining said constant voltages and said variable voltage, means for controlling the rate of said amplification by said control voltage when said variable voltage is less than the smaller of said constant voltages or greater than the larger of said constant voltages, and means for discontinuing said control voltage when the value of said variable voltage is between the values of said constant voltages.

15. In an electrical receiving set, a source of constant voltage, means for amplifying the signals received, means for obtaining a voltage which varies with the intensity of said signals, means for obtaining a control voltage by combining said constant voltage with said variable voltage, means for controlling the rate of said amplification by said control voltage when said variable voltage is less than said constant voltage, and means for discontinuing said control voltage when said variable voltage is greater than said constant voltage.

16. In an electrical receiving set, two sources of constant voltage of different values, means for amplifying the signals received, means for obtaining a voltage which varies with the intensity of said signals, means for obtaining a control voltage by combining said constant voltages with said variable voltage, means for controlling the rate of said amplification by said control voltage when said variable voltage is less than the smaller of said constant voltages or greater than the larger of said constant voltages, and means for discontinuing said control voltage when the value of said variable voltage is between the value of said constant voltages.

17. In an electrical receiving set, means for amplifying the signals received, means for deriving a voltage which represents a certain proportion of the intensity of the carrier wave, means for rectifying said carrier wave, means for obtaining a voltage which varies with the intensity of the rectified signals, means for obtaining a control voltage by combining said representative voltage with said variable voltage, means for controlling the rate of said amplification by said control voltage when said variable voltage is less than said representative voltage, and means for discontinuing said control voltage when said variable voltage is greater than said representative voltage.

18. In an electrical receiving set, means for amplifying the signals received, means for deriving a voltage which represents a certain proportion of the intensity of the carrier wave, means for rectifying said carrier wave, means for obtaining a voltage which varies with the intensity of the rectified signals, means for obtaining a control voltage by combining said representative voltage with said variable voltage, means for controlling the rate of said amplification by said control voltage when said variable voltage is greater than said representative voltage, and means for discontinuing said control voltage when said variable voltage is less than said representative voltage.

19. In a system for transmitting signals of variable intensity, a receiving circuit, means for setting up a high standard of intensity which is greater than the average intensity of said signals, means for setting up a low standard of intensity, means in said receiving circuit for amplifying said signals at a constant rate of amplification when the intensity of said signals is between said standards, and means for changing said rate of amplification when the intensity of said signals is not between said standards.

20. In an electrical receiving set, a source of constant voltage, means for amplifying the signals received, means for obtaining a voltage which varies with the intensity of said signals, means for obtaining a control voltage by combining said constant voltage and said variable voltage, means for controlling the rate of said amplification by said control voltage when said variable voltage is greater than said constant voltage, and means for discontinuing said control voltage when said variable voltage is less than said constant voltage.

21. In a system for transmitting signals of variable intensity, a means of amplifying the intensity of said signals, means for setting up a standard of intensity which is less than the average intensity of said signals in said amplifying means, automatic means for progressively increasing said rate of amplification as the intensity of said signals decreases below said standard of intensity, means for amplifying said signals which is representative of the intensity of said carrier wave, means for amplifying said signals, and means for automatically changing the rate of said amplification according to the intensity of said signals as compared with the intensity of 5 said carrier wave.

JAMES L. GETAZ. 

